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Equipment Discussions >> Binoviewers

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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6141582 - 10/16/13 07:04 PM Attachment (18 downloads)

For the Clicklock, just insert a ruler into the rear of the Clicklock and let it go until it touches the flat at the rear end of the SCT's rear port. Now, measure from the flat at the rear of the SCT port to the end of the Clicklock. This should be about 34mm to 36mm.

For the diagonal you need to make two measurments.

Just lay the ruler along the side of the mirror box and measure from the front to the where you think the front center of the mirror is at. Unless you are willing to touch the mirror itself, this is really the only way to do it.

Then, measure from the center of the mirror to the top of the mirror box.

Finally, measure form the top of the mirror box to the bottom of the Quick Connect ring (the BV light path includes the dovetail I think).

Yellow in pic... Notice that from front to center, about 1.27" front to center, and another 1.27" center to top of mirror box, for a total of about 2.54" or about 64mm just for the mirror box on the diagonal in the picture.

From the top of the mirror box to the top of the eyepiece holder on my diagonal is another 1.5" or another 38mm

You of course do not have this top piece (consistent with my advice to not use a standard 2" diagonal), but my entire light path for the 2" diagonal is about 92mm.

You though may be at the 54mm or maybe even shorter which would be really excellent for a 2" diagonal configuration.

So, for you, you would add the Clicklock, mirror box, and top of the box to the bottom of the quick connect ring, then add 123mm to that..


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141610 - 10/16/13 07:18 PM

My bet is that the Clicklock is going to be 35mm or so, and 54mm or so for the diagonal for a total of 89mm.

The powerswitch I think is 18m and the filter box looked like another 15mm or so, with some kind of attachment, so that would be 10mm.

Add the 123mm for the Mark V, and I get a total of 255mm.

If that is the case, it puts you 95mm over the point where I think my scope starts to loose aperture (160mm) and in my scope, this much back focus would cut me to about 7.1".

So, my guess is that either I have not estimated your total path well and you are shorter than this, or for some reason, my scope is loosing aperture with a bit less back focus than you are.

But I was guessing on your back focus really, and my formula is not exact, just an approximation (2.5mm for loss for every 10mm of back focus).

In fact, now that I am thinking about it, I have been saying 10mm for 2.5mm of aperture loss, but in fact, it may be 11mm and I just used 10mm to make it easy for people to remember.

This would give .85 aperture loss and this is closer to what you are getting, so my mistake for using 10mm as a convenience.

I just thought when people were dealing with 20mm or 30mm light path change, it would just be a little rounding error.

We can do the math when we get your numbers...


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141653 - 10/16/13 07:38 PM

I had this thought too.

Some of the difference in the reducer measurement may be due to the fact that my light path was almost 280mm the first time I measured. I was using a Clicklock, 2" diagonal with eyepiece holder, a powerswitch and a BV with a light path of about 130mm. Total was almost 280mm, so my system was already working at a much longer focal length and maybe my reducer measurement was affected by this.

Perhaps because you are using the reducer with a shorter light path BV, you don't need as much mirror travel.

I bet that is the difference. One would not think that 7mm light path would matter between the reducer and the eyepiece field stop, but it could mean less mirror travel in reducer mode.

So, a wild car. I was using Denks....

The difference could amount to .1" of aperture and that tallies good with my .4" to .5" loss for the reducer in my configuration vs. .3 in your... I had a much longer focal length to start because of the longer light path, and my BV was longer light path than the configuration with the Mk V.

That is why I tell people that they need to measure...



Edited by Eddgie (10/16/13 09:21 PM)


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tonyt
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141707 - 10/16/13 08:05 PM

On a related issue: WRT minimizing the binoviewer light path and eyepiece field stops, Sterling plossls are one of the worst eyepieces to use needing a lot of in-focus. Ortho's are one of the best, with around 20mm difference in the focus position compared to the Sterlings and Televue plossls and Panoptics are good with about 15mm difference in focus position compared to the Sterlings.

I wonder where the field stop of the Denk eyepieces is compared to others?


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6141850 - 10/16/13 09:31 PM

Yes, the Telvue 40 field stop is right at the bottom of the barrel, so they take the least amount of infocus.

35mm Ultimas are hard to understand. They have a field stop near the bottom like the TVs, but take far more in-travel.

Anyway, it could be a factor if HowardK is using an eyepiece that takes less in-travel.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6142288 - 10/17/13 05:16 AM

Eddgie

Cliklok visual back.....35mm
WO 2" diagonal.......88mm
Power/filterswitch.....63mm
Mkv..........123mm

Total.....309mm
I use 16mm NAGLERS pretty much all the time.

Loooong light path eh?


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6142537 - 10/17/13 09:42 AM

Ok, then there has to be some issue with my particular scope.

When I used 280mm, I was working at less than 7" even straight through.

So, my information is wrong and I will have to stop giving it out.

Perhaps they have changes something in the design so that the scope does not loose apeture until 200mm, which is the way the old C8 was set up.

I was under 6.5" with low power arm so again, much worse result than you are getting though I was also using a different binoviewer and I wonder if the binoviwer itself was somehow contributing to the differnce???

Again though, that is why I tell every one that if they really want to know, they need to measure for themselves.

So, has to be something different in my particular EdgeHD, which was one of the first delievered to the US or something with the Denk II that I used for these measurments.

But in the C14, the result was similar in that I was reduced to 12.5" with reducer in a 2" configuration, and improved to 13.5" with reducer by going to T2 prism and 13.9 straight through (full apeture with the Mark V and with the Binotron used with just the prism and no powerswitch.

I am happy with it now though, but you clearly have a better functioning system than I had.

If someone using a Denk II withs a 2" diagonal and power switch could make the measurement, then we would know for sure if the difference is in the EdgeHDs or perhaps an issue with the Denk II itself.

You are still loosing apeture of course, but much less than my "simple formula" would have calculated.

Has to be an answer, but we may never know...

Once again, people should measure if it matters to them.

You are lucky though. That is not nearly as bad as I would have calculated, so my data appears to be fautly, but don't know if it was becasue of some difference in the scope, or difference in the Binoviewer being used....

Edited by Eddgie (10/17/13 09:52 AM)


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6142661 - 10/17/13 10:47 AM

The more I think about this, the more puzzled I am.

I have done this measurement with three different scopes.

With the C5, my apeture reduction using a 2" power switch system and 30mm visual back was something like this (and I don't have the numbers, just going from memory).

With the 2" diagonal and PS in the C5

99mm In low power, something like 112 in straight though, and something like 119 in high power.

With the 1.25" diagonal, these went to 110mm in low power to something like 119mm with straight though and something like 123mm in high power.

And for the C14, it was much the same.

I think with 2" it was something like 12.6 in low power, 13.4 in straight though and 13.9 in high power.

With 1.25" it was something like 13.5" in low power, 13.9 straight though, and I did not measuer in high because I was sure it would be full apeture.

And of course the EdgeHD 8" was even worse than these.

So I am really struggling to understand why the result is so different.

The C5 was loosing 1.1" (a bit more than you) but I had a 10mm longer light path and the C14 was not that much different from you.

But muy EdgeHD 8" is clearly not working the same, while yours is working even better than any of my scopes did.

Some of it might be some difference in the binoviewrers, but some of it has got to be some issue with my EdgeHD 8".

I still beleive that keeping the light path short is beneficial, but I have to back off on providing any kind of general guideline now, and instead just suggest to people that if it matters to them, they need to measure for themselves.

I wish I knew why the discrepencey was so large though.

And when I thought about it, when you were configured about the same as I was using the same binoviewer, you were still working at less than full apeture, but still with a much longer light path, so that would rule out the binoviewer.

My light path with the 10mm/T2/Mark V is 171mm, and I am only getting 200mm. You have 60mm more than I do and you are still working at the same apeture.

Has to be something with my EdgeHD 8". There really isn;t any other explination, and this would mean that what I have been telling people is very innacurate.

I have though been careful to tell people that they should measure for themselves, so at least I can say that I was open to accepting an error in my data.

Edited by Eddgie (10/17/13 10:54 AM)


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6142855 - 10/17/13 12:29 PM

Eddgie

I am going to recheck my aperture measurements again in reduction mode and straight thru

Just to be certain


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6143611 - 10/17/13 07:53 PM

No, you have checked them twice already. If you got the same thing both times, I think that is pretty reliable.

I think it must be something with my scope.

Your result is far more consistent with the standard SCT and I was really quite surprised to see the reduction starting so early on the EdgeHD 8".

So, my bet is that your outcome would be the same. Has to be some difference in my scope.

Maybe my baffle is sticking out further or something.


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tonyt
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6144239 - 10/18/13 04:09 AM

I did a measurement with my 8" Edge to add to the list.

Baader Cliklock visual back, 1.25" Tak prism diagonal, WO binoviewer and 25mm Televue plossls gave an aperture of 192mm (between 7.5" and 7.6")


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6144466 - 10/18/13 09:18 AM

That is interesting because that between our measurments.

If your visual back is 35mm, a standard 1.25" diagonal is about 70mm, and the WO is about 110mm, so you are at about 215mm light path.

If we loose 2.5mm for every 10mm of back focus (and this is aproximate, you are starting to loose aperture at about 175mm.

This seems much closer to where I loose aperture than where HowardK does. Interesting...

With his setup, it would appear that he is not loosing aperture until 230mm of back focus.


Very strange.

My guess is that his baffle tube is shorter than ours. I would guess this because it is the primary baffle that hits the light cone first as the mirror is moved forward.

Our baffles may be about the same length, but perhaps is is 5mm or 6mm shorter.

Very interesting. Wish we could measure baffles of all three to see.


So, for you, if you were to use a 2" diagonal, you would also drop below 7" I think.

It would appear thought that there is some variability, and for this reason, people should measure.

Also, my formula (10mm = -2.5mm loss) may not be accurate.

Interesting....


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tonyt
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6144514 - 10/18/13 09:43 AM

Just eyeballing the baffle, the length of the baffle sticking out past the mirror slide safety ring appears to be similar to or slightly longer than the width of the end of the baffle.

Edited by tonyt (10/18/13 09:44 AM)


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6145289 - 10/18/13 05:33 PM

Have you measured your light path? I just estimated, but I could be wrong on the diagonal. Most 2" diagonals though are about 70mm light path.

I am not sure if looking at the baffle that is sticking out in front of the mirror is reliable, because the mirror would have to be fully to the rear.

I think that the difference would be where the baffle is threaded into the rear cell. If my baffle is not screwed in as far as yours or Howards, then he could push the mirror further forward.

But the difference here is pretty extreme. Even with over 300mm, Howard is loosing only .7", and if the formula I have is even partly correct, I would have thougth that he would be under 7".

You are much closer to me. When my light path was 191mm, I was at 7.7". Taking off the Televue short back (30mm) and going to the 10mm SCT to T2 got me to 7.85" so just a bit short of .2" for about 20mm of light path.

The only possible explanation is that his baffle is screwed in deeper.


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tonyt
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6145413 - 10/18/13 06:54 PM

Quote:

The only possible explanation is that his baffle is screwed in deeper.




There could have been a manufacturing change or there could be errors in measurement - we have 3 different people doing the measuring (not meaning to be impolite, it's just a possibility). It would be useful if another owner of a recently purchased scope could do a measurement - mine is 2 or 3 years old, purchased second hand (very nice optics though ).

Edited by tonyt (10/18/13 06:59 PM)


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6145752 - 10/18/13 10:32 PM

Well, there is always the possibility of error in the measurements, but I have done mine many times, and get pretty consistent readings.

Also, I have measured C5 and C14 as well, and my "Formula" (which may not be that accurate) was based on the fact that all three tended to behave the same way once aperture loss started.

And I have measured in 2" and 1.25", and the result was always the same. If there was aperture reduction, for about every 10mm or 11mm of back focus I could cut out, I restored about 2.5mm of aperture (.1").

These measurements are kind of hard to take though, and are not all that exact, but overall, this is about the way it averaged out for me

I think that this latest measurement is closer to mine though.

Would be helpful though is we knew your light path. I am only guessing, and there is nothing like a ruler to make sure.

Also, I am estimating the WO binoviewers to be similar to the Maxbright, but I don't know if that is the case. They are about the same size though, so I expect that 110mm is about right, and I doubt that they are shorter than the Maxbright, but they could be a bit longer.

I think going with 110mm is about right.

Not sure about the Tak diagonal, but most 1.25" diagonals are between 60mm and 70mm.

Assuming that the prism is about the same size of the T2, then the path though the housing is most likely about 40mm, and most of these have an eyepiece holder about 25mm, so I would be surprised if it was much shorter than 65mm, and would bet that it is a bit longer than this.

So, it would be good to have a close measurement.

My EdgeHD 8" is also a few years old. One of the first sold.


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tonyt
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6145882 - 10/19/13 12:14 AM

My light path:
Using measurements others have done for the diagonal and bino rather than taking my own measurements in a refractor, I come up with 207mm from the end of the rear cell threads.

Tak 1.25 diagonal: 64mm
WO Binoviewer: 108mm
Cliklock VB: 35mm (not including the part that screws onto the rear cell threads)

Edited by tonyt (10/19/13 12:22 AM)


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6146357 - 10/19/13 10:26 AM

Interesting.

See, this is much closer to what I get in terms of aperture loss.

I am at 171, and I am loosing .15", but I calculated about 2.5mm for every 10mm of added length.

Your length is about 35mm more than mine, so this would suggest an additional (3.5 x 2.5mm) an extra 8.75mm of loss over my .15mm, for a total of 8.9mm of loss.

And that would put you right at (203 - 9) 194mm.

Now the difference of 2mm is 1% of the total aperture, and this I think 1% difference is within the margin of error for the test (this is what I think other testers have come up with and I believe that the diffraction caused by the light coming out of the baffle actually does make the test difficult to interpret with 100% accuracy).

It would appear that your scope is working almost exactly the same as mine though, with aperture loss starting at maybe a tiny bit longer back focus than my own, but in general agreement.

This would indicate that aperture reduction is indeed starting on our scopes at about 165mm and that every 10mm or 11mm of additional back focus takes 2.5mm of aperture.

I am at a complete loss to explain HowardsK's superb result, but it can only be a factor of the baffle being shorter. There really is no other explanation.

And it would have to be a lot shorter, because even the standard C8 looses more aperture than he is loosing.

I am perplexed how his instrument could have such a fantastic result though as compared to ours.

If you were to measure with a 2" diagonal, it would be interesting to know what your result was though.

But I would not expect you to do that. I know from first hand experience how tedious it is to do these measurements.

I did about 6 different measurements on the C14 and it was simply to tedious that I stopped after that, but not before I had a pretty good ideal of the situation (aperture reduction at about 200mm, and again, about .1" per 10mm of additional light path)

Thanks for reporting this though. We now have three data sets and they all have one thing in common. All three scopes were loosing aperture in the configurations measured.

I feel better (at your expense) about my own efforts to bring awareness to the forum members about the potential of aperture loss, but clearly, I am relieved that I have also included an urging for people to make their own measurements.

In your case, shortening further may not bring a noticeable improvement in performance, but it re-enforces my warning on these scopes (or at least perhaps the earlier versions) that one should be careful to avoid excessive back focus, and that to really know how an individual scope will behave, it is best to measure for one's self.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6146541 - 10/19/13 11:52 AM

I checked my aperture in reduction mode...it is...

175mm at infinity focus.

Will recheck straight thru measurement tonight.

My 8" Edge is 6 months old.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6155930 - 10/24/13 04:52 PM

For Eddgie

At infinity focus...Cliklok visual back.....35mm
WO 2" diagonal.......88mm
Power/filterswitch.....63mm
Mkv..........123mm

Total.....309mm

Aperture...
Reducer mode = 175mm
Straight thru = 186mm


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